The present invention relates to a centralized control architecture for operating a plasma arc system.
Plasma arc systems are widely used for cutting metallic materials and can be automated for automatically cutting a metallic workpiece. In general, a plasma arc system includes a plasma arc torch, an associated power supply, a remote high-frequency (RHF) console, a gas supply, a positioning apparatus, a cutting table, a torch height control, and an associated computerized numeric controller. FIG. 1 shows an example of a plasma arc system.
In operation, a user places a workpiece on the cutting table and mounts the plasma arc torch on the positioning apparatus to provide relative motion between the tip of the torch and the workpiece to direct the plasma arc along a processing path. The user provides a start command to the computerized numeric controller (CNC) to initiate the cutting process. The CNC accurately directs motion of the torch and/or the cutting table to enable the workpiece to be cut to a desired pattern. The CNC is in communication with the positioning apparatus. The positioning apparatus uses signals from the CNC to direct the torch along a desired cutting path. Position information is returned from the positioning apparatus to the CNC to allow the CNC to operate interactively with the positioning apparatus to obtain an accurate cut path.
The power supply provides the electrical current necessary to generate the plasma arc. The power supply has one or more dc power modules to produce a constant current for the torch. Typically, the current can be set to discreet values. The power supply has a microprocessor, which regulates essentially all plasma system functions, including start sequence, CNC interface functions, gas and cut parameters, and shut off sequences. For example, the microprocessor can ramp-up or ramp-down the electrical current. The main on and off switch of the power supply can be controlled locally or remotely by the CNC. The power supply also houses a cooling system for cooling the torch.
The gas console controls flow of plasma and shield gases to the torch. The gas console houses solenoid valves, flow meters, pressure gauges, and switches used for plasma and shield gas flow control. The flow meters are used to set the preflow rates and cut flow rates for the plasma and shield gases. The gas console also has a multi-inlet gas supply area where the required plasma and shield gases can be connected. A toggle switch can be used to select the plasma gases. The plasma and shield gases are monitored by gas pressure gages. In order to operate the gas console, all settings must be manually selected.
The RHF console houses a high frequency starting circuit that is used to fire the torch. The RHF console also houses a cathode manifold used to interface power and coolant leads between the power supply and the torch. The power and coolant leads and a pilot arc lead make up a shielded torch lead set which connects with the torch. In addition, gas lines are also supplied to the torch to supply gas.
The torch height control sets the height of the torch relative to the work piece. The torch height control, typically, has its own control module to control an arc voltage during cutting by adjusting the standoff, (i.e., the distance between the torch and the work piece), to maintain a predetermined arc voltage value. The torch height control has its own external control module to control the standoff. The torch height control has a lifter, which is controlled by the control module through a motor, to slide the torch in a vertical direction relative to the work piece to maintain the desired voltage during cutting.
The plasma arc torch generally includes a torch body, an electrode mounted within the body, passages for cooling fluid and cut and shield gases, a swirl ring to control the fluid flow patterns, a nozzle with-a central exit-orifice, and electrical connections. A shield can also be provided around the nozzle to protect the nozzle and to provide a shield gas flow to the area proximate the plasma arc. Gases applied to the torch can be non-reactive (e.g. argon or nitrogen) or reactive (e.g. oxygen or air).
In operation, the tip of the torch is positioned proximate the workpiece by the positioning apparatus. A pilot arc is first generated between the electrode (cathode) and the nozzle (anode) by using, for example, a high frequency, high voltage signal from the RHF console. The pilot arc ionizes gas from the gas console passing through the nozzle exit orifice. As the ionized gas reduces the electrical resistance between the electrode and the workpiece, the arc transfers from the nozzle to the workpiece. The torch is operated in this transferred plasma arc mode, which is characterized by the conductive flow of ionized gas from the electrode to the workpiece, to cut the workpiece.
The plasma arc system as described above has high cycle time. First, a torch operator must know some basic cutting parameters, such as the material to be cut, the thickness of the workpiece, and the plasma gas to be used. Then, the operator must review a series of tables found in books to manually set many parameters such as the power settings on the power supply or the gas flow on the gas console. Having to look tip additional parameters takes time and may result in operator error as manual input can be inaccurate.
In addition, some components such as the torch height control and the power supply have their own control, which can be redundant. Furthermore, there is no feedback mechanism between the components of the plasma arc system to optimize the operation of the plasma arc system.
The present invention relates to a control architecture for a plasma arc cutting system. In particular, the invention relates to a centralized control architecture for a plasma arc cutting system, in which the xe2x80x9cintelligencexe2x80x9d of the system is integrated into a single controller.
In one aspect, the invention features a method of controlling an integrated plasma arc system. According to one embodiment of the method, a first group of process parameters are input into a controller. A second group of process parameters are generated based on the first group of process parameters. At least one command signal is provided from the controller to at least one auxiliary device to control an output parameter generated by the at least one auxiliary device. At least one auxiliary device is either a power supply or an automatic process controller. The output parameter generated by the auxiliary device is detected and the command signal provided to the auxiliary device is adjusted based on the detected output parameter.
At least one auxiliary device can be the automatic process controller. The pressure of gas exiting the automatic process controller can be detected and the command signal provided to the automatic process controller for controlling the gas flow can be adjusted based on the pressure. At least one auxiliary device can be the power supply. A feedback signal generated by the power supply indicative of an arc voltage at the plasma arc torch can be detected and the command signal provided to the power source for controlling a current output can be adjusted based on the feedback signal.
At least one auxiliary device can include a first auxiliary device and a second auxiliary device. A first output parameter generated by the first auxiliary device can be detected and the command signal provided to the second auxiliary device can be adjusted based on the first output parameter. For example, the first auxiliary device can be the automated process controller and the second auxiliary device can be the power supply. The pressure of an outlet gas exiting the automated process controller can be detected and the command signal provided to the power supply for controlling an output current can be adjusted based on the pressure. A feedback signal generated by the power supply indicative of an arc voltage of the plasma arc torch can be detected and the command signal provided to the automatic process controller for controlling the gas flow can be adjusted based on the feedback signal. Alternatively, the first auxiliary device can be the power supply and the second auxiliary device can be a torch height controller. The feedback signal generated by the power supply can be detected and the command signal provided to the torch height controller for controlling a standoff can be adjusted based on the feedback signal.
The method of controlling the integrated plasma arc system can also include the step of monitoring a life of a consumable of the plasma arc torch. The life of the consumable can be monitored and the command signal provided to at least one auxiliary device can be adjusted based on the monitored life of the consumable. The pressure of gas exiting the automatic process controller and/or the arc voltage at the torch can be compared to a reference value to determine the wear of the consumable. The flow rate of gas provided to the plasma arc torch and/or the cutting current can be adjusted to compensate for the wear of the consumable.
In another aspect, the invention features a method of controlling an operation of a plasma arc torch system, which includes an automatic process controller in electrical communication with a computerized numeric controller and in fluid communication with a plasma arc torch. The automatic process controller has at least one valve and at least one sensor. According to the method, a command signal is provided from the computerized numerical controller to the valve to control a flow of at least one gas to the plasma arc torch. A condition of the gas exiting the automatic process controller is monitored using the sensor. The command signal provided to the valve is adjusted based on the monitored condition.
In one embodiment, a first command signal is provided to a first valve to control the flow of a cut gas and a second command signal is provided to a second valve to control the flow of a shield gas. The pressure of the cut gas is monitored using a first pressure transducer and the pressure of the shield gas is monitored using the second pressure transducer. The first command signal provided to the first valve is adjusted based on the pressure of the cut gas monitored by the first pressure transducer. The second command signal provided to the second valve is adjusted based on the pressure of the shield gas monitored by the second pressure transducer.
In one aspect, the invention features a controller for an integrated plasma arc system. The controller includes an input module, a reference module, at least one interface module, and a detection module. The input module receives a first group of process parameters from a user for operating the plasma arc system. The reference module generates a second group of process parameters for operating the plasma arc system based on the first group of process parameters. At least one interface module interfaces with at least one auxiliary device of the plasma arc system and provides at least one command signal to the auxiliary device to control an output parameter generated by the auxiliary device. At least one of the auxiliary device is a power supply or an automatic process controller. The detection module monitors the output parameter generated by the auxiliary device and adjusts the command signal provided to the auxiliary device.
The auxiliary device can be a power supply and the detection module can monitor a current output generated by the power supply. The auxiliary device can be an automatic process controller for controlling gas flow to the plasma arc torch and the detection module can monitor pressure of the gas and adjust the command signal provided to a valve in the automatic process controller based on the pressure. The gas can be a cut gas and/or a shield gas.
In another aspect, the invention features a control system for controlling an operation of a plasma arc system. The control system includes an automatic process controller and a computerized numerical controller (CNC) in electrical communication with the automatic process controller. The automatic process controller includes at least one valve for controlling a flow of at least one gas to a plasma arc torch and at least one sensor for monitoring a condition of the gas. The CNC generates at least one command signal for operating at least one valve, receives the condition monitored by at least one sensor, and adjusts the command signal based on the condition monitored by the sensor.
The automatic process controller can include a first manifold for controlling flow of a cut gas and a second manifold for controlling flow of a shield gas. Two cut gases can be mixed in the first manifold. The automatic process controller can include a first proportional flow control valve positioned upstream of the first manifold for controlling a cut gas flow to the first manifold and a first pressure transducer positioned downstream from the first manifold to measure pressure of the cut gas exiting the first manifold. The automatic process controller can include a second proportional flow control valve positioned upstream of the second manifold to control a shield gas flow to the second manifold and a second pressure transducer positioned downstream from the second manifold to measure pressure of the shield gas exiting the second manifold. The first proportional flow control valve can be adjusted based on the pressure of the cut gas measured by the first pressure transducer. The second proportional flow control valve can be adjusted based on the pressure of the shield gas measured by the second pressure transducer.
In another aspect, the invention features an integrated plasma arc system. The system includes a controller, a power source, a plasma arc torch, an automatic process controller, and a torch height controller. The power source is in electrical communication with the controller. The power source generates an electrical current sufficient to form a plasma arc. The plasma arc torch is in electrical communication with the power source through a torch lead. The automatic process controller is in electrical communication with the controller. The automatic process controller is positioned to control delivery of gas from the power source to the plasma arc torch. The torch height controller is in electrical communication with the controller. The torch height controller is positioned to control a standoff between the plasma arc torch and a workpiece. The controller is physically remote from the power supply, the torch height controller and the automatic process controller. The controller controls, monitors and adjusts an output parameter of each of the power supply, the automatic process controller and the torch height controller for operation of the plasma arc system.
In one embodiment, the system also includes a table and a drive system for moving the plasma arc torch over a cutting surface of the table. The controller provides a command signal to the drive system to position the drive system and receives a feedback signal from the drive system to monitor a position of the drive system.
In another aspect, the invention features a plasma arc system which includes a power source and a controller in electrical communication with and physically remote from the power source. The power source generates an electrical current sufficient to form a plasma arc in a plasma arc torch. The controller controls, monitors, and adjusts the electrical signal generated by the power source.
The power source can include an input, a switch, a main transformer, at least one dc power module, and torch ignition circuitry. The input receives an input signal. The switch can be in electrical communication with the input and the controller. The switch can receive a switch command signal from the controller to open or close the switch. The main transformer can be in electrical communication with the switch to receive the input signal when the switch is closed and generates an AC output signal. The dc power module can be in electrical communication with the main transformer and the controller. The dc power module can receive the AC output signal from the main transformer and a dc power module command signal from the controller. The dc power module can generate a rectified DC output signal and provide a dc power module feedback signal to the controller. The torch ignition circuitry can be in electrical communication with the dc power module to receive the rectified DC output signal and generate the electrical current sufficient to form the plasma arc.
The controller can provide a command signal corresponding to a desired rectified DC output signal to the dc power module. The controller can provide a command signal to the dc power module to ramp up or ramp down the rectified output signal.
The power supply can also include a transformer in electrical communication with the input and the controller and a switching supply in electrical communication with the control transformer and the controller. The power supply can also include a heat exchanger. The heat exchanger can have the same electrical potential as the electrode of the plasma arc torch. The heat exchanger includes a coolant, and the controller can monitor the flow rate, the flow level, and/or the temperature of the coolant. The power supply can also include a voltage feedback card. The voltage feedback card can be in electrical communication with the torch ignition circuitry and the controller. The voltage feedback card can monitor the rectified DC output signal from the dc power module and provide a voltage feedback signal to the controller. The voltage feedback card can signal the controller when a pilot arc is established, and/or when cutting arc is established.
In another aspect, the invention features a method of controlling a power supply of a plasma arc system which includes a controller in electrical communication with the power supply. According to the method, a command signal is provided from the controller to the power supply to generate an electrical current sufficient to form a plasma arc in a plasma arc torch. The electrical current generated by the power supply is monitored. The command signal provided from the controller to the power supply is based on the electrical current monitored.